The present invention relates to a needle selector for a knitting machine having incorporated therein a pattern-knitting apparatus of electronically controlled type in which electromagnets are operative in response respectively to needle-selecting signals to carry out needle selection.
FIGS. 8 and 9 show, as a first example, a known needle selector for a circular knitting machine, as disclosed, for example, in Japanese Patent Publication No. 42-20439 filed claiming the priority rights based on West German Application Nos. M64179 and M64421 both filed on Mar. 6, 1965, and corresponding to British Specification No. 1,112,59. In the known needle selector, a multiplicity of needle-selecting jacks are fitted respectively in needle grooves provided in a rotary cylinder. The jacks have their respective lower ends remote from respective needles, which serve respectively as fulcrums. Each jack has, adjacent its upper end, a butt engageable with a cam face. A spring is provided on the rear side of each jack for biasing the same to bring its butt into engagement with the cam face. A control pin is controlled in operation by a control electromagnet, to carry out needle selection. FIGS. 10 and 11 show a second example as disclosed in Japanese Patent Publication No. 53-1865, in which two kinds of jacks having their respective projections different in position from each other are fitted in each of needle grooves provided in a rotary cylinder. Permanent magnets are arranged on a stationary side at positions corresponding respectively to upper and lower portions of the jacks. The jacks balance under the magnetic force about respective fulcrums at the centers of the respective jacks. Control electromagnets are mounted at positions corresponding respectively to the projections of the respective jacks. The operation of the electromagnets is controlled in response to a signal outputted from a program to destroy the balance, thereby carrying out needle selection.
As described above, the arrangement of the first example is such that the control pin and the spring for urging the jack against the cam face are employed, and friction force due to the pressure of the spring on the rear side of the jack is utilized to prevent the latter from being relieved. Because of such arrangement, a high spring force is required for the control pin to bias the jack against the spring force of the jack spring, resulting in premature wear and fatigue of the control pin. In addition, the high spring force of the control pin exerts a bad influence on the balance of the magnetic force of the needle-selecting electromagnets with respect to demagnetizing solenoids for improving the responsibility of the magnets, thereby making the needle-selecting unit complicated in structure. Moreover, the arrangement of the first example is inconvenient to effect control of three positions including a welt position, a tuck position and a knit position. On the other hand, the above-described second example requires highly accurate management in processing and assembling, in order to accurately maintain contact between the magnets and the jack attracting faces. The management includes management of distances from the fulcrum of each jack to the opposite ends thereof, and management of gaps at the cam face. The above management also includes management of an accuracy of the position of the magnet solenoids. Thus, the second example forces considerable burden upon an operator. In addition, since the second example is so arranged as to balance the magnetic force, strong magnetic force is required for the control electromagnets to separate the jacks from the permanent magnets against the magnetic force thereof in order to control the jacks. This increases the size of the magnets, causing problems in the speed responsibility such as rise of the magnetic force, remanence and the like. Thus, the combination of the magnets is made complicated. Furthermore, in order to maintain the requisite accuracy, it is inevitable for the second example that the construction becomes complicated and the overall size becomes large. This makes it difficult for the needle selector to take a three position structure which requires incorporation of two needle selecting controls in the cam arrangement of one knitting course-one feeder. Such electronically controlled needle selection is not preferable, because the three position structure is formed by two sets of knitting cams so that the number of feeders is reduced by half to lower the productivity. Moreover, it is impossible to apply the second example to an electronic control of operation of a dial.